The present invention relates to a magnetic tunnel junction and its fabrication method, and more particularly, to a magnetic tunnel junction with a bilayer hard mask that prevents degradation of the performance of a magnetic tunnel junction (MTJ) structure.
MRAM is a non-volatile random access memory technology in which data is stored by magnetic storage elements. These elements are typically formed from two ferromagnetic layers, each of which can hold a magnetization, separated by a thin dielectric layer. One of the two layers is a permanent magnet set to a particular polarity; the other layer's magnetization can be changed to match that of an external field to store memory. Such a configuration is known as magnetic tunnel junction (MTJ).
In leading-edge or neuromorphic computing systems, a MTJ structure (or pillar) is typically embedded within a back-end-of-the-line (BEOL) structure, a metal hard mask is typically formed above a multilayered MTJ structure, and the metal hardmask is used as an etch mask to provide the MTJ structure.
Current semiconductor manufacturing techniques of an MTJ bit, i.e., a MTJ stack, requires patterning of the fixed layer, free layer, and tunnel layer. However, current processing techniques for patterning of MTJ stacks encounter issues with redeposition, as the stack is often etched using physical sputtering.
However, redeposition of conductive metal on a sidewall of the MTJ device, particularly across the tunnel barrier, can create a short circuit.
Moreover, as the metal hardmask often doubles as the top electrode in an MTJ cell, it is also a source of potential redeposition. This layer is exposed to the stack etch for the entire duration and thus can serve as a source of potential metal redeposition.